1. Field of the Invention
The present invention relates to a brake system of vehicles such as automobiles, and more particularly, to such a brake system in which it is judged as a part of control routine if the pressure sensors incorporated therein are operating normally or not.
2. Description of the Prior Art
In the modern electrically controlled brake systems of vehicles such as automobiles, having a basic construction that a wheel cylinder for applying a braking force to a wheel is supplied with a brake fluid compressed by a motor-powered pump through a pressure control circuit which includes an inlet control valve of a solenoid changeover type for selectively connecting or isolating the wheel cylinder to or from the pump and an outlet control valve of a solenoid changeover type for selectively connecting or isolating the wheel cylinder to or from a drain passage leading to a reservoir for the pump, so that the pressure supplied to the wheel cylinder is controlled by an on/off duty ratio of the inlet and outlet control valves, the brake control is basically dependent upon the detection of the brake fluid pressure actually supplied to the wheel cylinder, as the control is a feedback control, and therefore, in order to ensure a sound operation of such a brake system it is essential that the normal operation of pressure sensors incorporated in the pressure control circuit is effectively judged.
In Japanese Patent Laid-open Publication 8-26099, there is described an electric brake system of a four-wheeled vehicle in which the four of a pair of front wheels and a pair of rear wheels are braked by individual wheel cylinders powered by separate fluid pressure generation means operated under a control of a central electronic control unit with a feedback of the pressures of the respective wheel cylinders detected by corresponding pressure sensors, wherein the front pair of wheel cylinders and the rear pair of wheel cylinders are respectively connected by a connection pipe incorporating a changeover valve, so that a failure of one of the front pair or rear pair of pressure sensors is detectable by a comparison of outputs of the pair of sensors under an opening of the changeover valve, in addition to a diagnosis of comparing the output of each sensor with the pressure instructed thereto from the central control unit.
The above-mentioned prior art needs an additional arrangement of the connection pipes and the changeover valves.
In view of the above, it is a primary object of the present invention to provide a brake system for vehicles such as automobiles, also in the modern electrical type, in which a normal operation of pressure sensors installed therein is judged without any additional arrangement of a pipe and/or a valve therefor.
Particularly, it is a further object of the present invention to provide such a brake system which can judge a normal operation of a pressure sensor for the pressure of a brake fluid at the delivery of a pump forming the pressure source of the brake system, together with a normal operation judgment of a pair of pressure sensors for a pair of wheel cylinders of a front pair or a rear pail of wheels.
According to the present invention, the above-mentioned primary object is accomplished by a brake system of a vehicle having a pair of front wheels and a pair of rear wheels, comprising a brake pedal, a fluid reservoir, a motor-driven pump for pumping a fluid from the reservoir to an outlet port thereof, at least one pair of wheel cylinders for braking one of the front pair and the rear pair of wheels according to a supply of a fluid pressure thereto, a fluid circuit having a pair of inlet control valves for selectively connecting the pair of wheel cylinders respectively to the outlet port of the pump and a pair of outlet control valves for selectively connecting the pair of wheel cylinders respectively to the reservoir, brake control means for controlling a motor driving of the pump and opening/closing of the inlet and outlet control valves so as to supply a controlled fluid pressure to the pair of wheel cylinders, and pressure sensors including a pair of wheel cylinder pressure sensors for measuring fluid pressures of the pair of wheel cylinders, the brake control means comprising:
means for at least temporarily substantially fully opening the pair of inlet control valves, while substantially closing the pair of outlet control valves;
means for comparing output signals of the pair of wheel cylinder pressure sensors to judge if there is a first difference therebetween beyond a first predetermined threshold value; and
means for judging the pair of wheel cylinder pressure sensors to be both operating normally when the first difference is not larger than the first threshold value.
In such a brake system of a vehicle having a pair of front wheels and a pair of rear wheels, wherein the brake system comprises a brake pedal, a fluid reservoir, a motor-driven pump for pumping a fluid from the reservoir to an outlet port thereof, at least one pair of wheel cylinders for braking one of the front pair and the rear pair of wheels according to a supply of a fluid pressure thereto, a fluid circuit having a pair of inlet control valves for selectively connecting the pair of wheel cylinders respectively to the outlet port of the pump and a pair of outlet control valves for selectively connecting the pair of wheel cylinders respectively to the reservoir, and brake control means for controlling a motor driving of the pump and opening/closing of the inlet and outlet control valves so as to supply a controlled fluid pressure to the pair of wheel cylinders, it is possible to at least temporarily operate the brake system so as to apply a braking to the vehicle according to a depression of the brake pedal by a driver by supplying such a fluid pressure to the pair of wheel cylinders that is controlled to correspond to the brake pedal depression by way of a motor drive speed control of the pump, with the pair of the inlet control valves being substantially fully opened, while the pair of the outlet control valves being substantially closed, so that the pressure sensors provided for measuring the pressures of the pair of wheel cylinders are applied with a common pressure through the fluid circuit.
Such a manner of operation of the brake system that the fluid pressures of the pair of wheel cylinders are controlled according to the depression of the brake pedal by the driver by way of the speed control of the motor driving of the pump, with the pair of the inlet control valves being substantially fully opened, while the pair of the outlet control valves being substantially closed, may be only temporarily carried out at such a time when, for example, the brake pedal is depressed while the vehicle is not moving, or may be normally carried out during the driving of the vehicle.
Even in the latter case, the pair of inlet and outlet control valves are still required in order to incorporate a manual brake part in the brake system for an emergency purpose.
Further, when the fluid pressures supplied to the pair of wheel cylinders are controlled by the speed control of the motor driving of the pump, the brake control means may control one of the pair of outlet control valves such that the substantially closed condition thereof is modified so as to make an adjustment of the fluid pressures supplied to the pair of wheel cylinders.
By such a comparison between the outputs of the pair of pressure sensors, it is judged at least if both of the pair of sensors are operating normally, and therefore, if at least one of the pair of sensors is not operating normally. In the art herein concerned, it is practically essential and enough if the failure of any one of a plurality of sensors is judged, because it is very rare that two or more sensors fail at the same time, while when any one of the sensors has failed, the vehicle will be brought to a repair shop where it will be readily known which of the plurality of sensors has failed, while other sensors will also receive inspections for maintenance.
Further, the above-mentioned further particular object of the present invention is accomplished according to the present invention when the brake system of the above-mentioned construction further comprises a pump delivery pressure sensor for measuring a delivery fluid pressure of the pump, and the brake control means further comprise means for comparing an output signal of the pump delivery pressure sensor and the output signal of a first one of the pair of wheel cylinder pressure sensors to judge if there is a second difference therebetween beyond a second predetermined threshold value; and means for judging the pump delivery pressure sensor and the pair of wheel cylinder pressure sensors to be all operating normally when the first difference is not larger than the first threshold value, with the second difference being not larger than the second threshold value.
In the brake system of the above-mentioned construction, the brake control means may further comprise means for judging the pump delivery pressure sensor to be not operating normally when the first difference is not larger than the first threshold value, with the second difference being larger than the second threshold value.
In the brake system of the above-mentioned construction, the brake control means may further comprise means for judging a second one of the pair of wheel cylinder pressure sensors to be not operating normally when the first difference is larger than the first threshold value, with the second difference being not larger than the second threshold value.
In the brake system of the above-mentioned construction, the brake control means may further comprise means for judging the first one of the pair of wheel cylinder pressure sensors to be not operating normally when the first difference is larger than the first threshold value, with the second difference being larger than the second threshold value.
In the brake system of the above-mentioned construction, the brake control means may further comprise means for comparing the output signals of the pump delivery pressure sensor and a second one of the pair of wheel cylinder pressure sensors to judge if there is a third difference therebetween beyond the second predetermined threshold value; and means for judging the first one of the pair of wheel cylinder pressure sensors to be not operating normally when the first difference is larger than the first threshold value, with the second difference being not larger than the second threshold value.
In the brake system of the above-mentioned construction having the means for comparing the output signals of the pump delivery pressure sensor and the second one of the pair of wheel cylinder pressure sensors, the brake control means may further comprise means for judging the second one of the pair of wheel cylinder pressure sensors to be not operating normally when the first difference is larger than the first threshold value, with the second difference being larger than the second threshold value.
In the brake system of the above-mentioned construction, the pair of wheel cylinders may be those for braking the pair of front wheels, and the first and second threshold values may be substantially equal to one another.
In the brake system of the above-mentioned construction, the pair of wheel cylinders may be those for braking the pair of rear wheels, and the second threshold value may be larger than the first threshold value by an amount corresponding to a less braking of the rear wheels relative to the front wheels.